The costing of the shipping is calculated based on both the gross weight and the volumetric weight. Whichever is higher is called chargeable weight:

The gross weight is the actual weight of the shipment when put on a scale.

The volumetric weight of a shipment reflects the density of a package. Lower density means that the package is occupying a high volume while the actual weight is low. There are few ways to calculate the volumetric weight (in kg):

L(cm)xW(cm)xH(cm) / WF(weight factor)In most of the situations, Weight Factor is 6000 or 5000.